Turkish officials, led by the prime minister, Binali Yildirim, have initially blamed the Istanbul airport attack on Islamic State, and it is true that this latest murderous outrage closely resembles last October’s Isis bombing of a peace rally in Ankara that killed 103 people, the deadliest such attack in modern Turkish history.

Assuming the official claim turns out to be accurate, it once again raises the murky question of Turkish government attitudes towards the Isis militants who control or are contesting large swaths of territory adjacent to Turkey’s southern border with Syria and Iraq and are said to maintain networks of supporters inside Turkey.

The basic problem is that Recep Tayyip Erdoğan, Turkey’s president, believes indigenous Kurds in those areas and in south-east Turkey pose a bigger threat than does Isis. This perceived ambivalence has led to numerous accusations of tacit Turkish support for or, worse still, complicity in Isis’s activities since the group swept to prominence in 2014 – all flatly denied by Erdoğan and his ministers.

The mostly unproven accusations, listed in a research paper published by New York’s Columbia University, include claims that predominantly Sunni Muslim Turkey has covertly supplied, trained, financed and assisted the recruitment of Isis’s Sunni fighters in their battles with the Kurds, with Iraq’s Shia-led government, and with the Syrian government, which Turkey opposes.

Some of the accusations, such as the government’s direct arming of Isis, seem far-fetched. But other claims, including suggestions that Turkish middlemen were involved in lucrative Isis oil smuggling from Iraq to Turkey, are widely believed.

Kemal Kiliçdaroglu, leader of the main Turkish opposition Republican People’s party (CHP), produced documents and transcripts in 2014 purporting to show that Turkey supplied weapons to terror groups inside Syria. It was suggested the arms went to ethnic Turkmen fighters opposed to Syria’s leader, Bashar al-Assad, not Isis.

Erdoğan’s government has also been accused of supporting – by what means is unclear – an al-Qaida-affiliated Syrian rebel force, Jabhat al-Nusra, which is said to be backed by Turkey’s ally Saudi Arabia but which is proscribed as a terrorist outfit by the US and Britain, also Ankara’s allies.

When in May 2015 the Cumhuriyet daily published material and footage alleging that Turkish MIT intelligence agents had tried to smuggle arms into Syria and been intercepted by border guards, the paper’s editor, Can Dündar, was arrested and charged with security offences and the border guards were dismissed. Such official pressure tactics have inhibited subsequent independent reporting.

Specific allegations aside, Erdoğan is accused by his opponents of indirectly helping Isis by thwarting, and refusing to support, efforts by Kurdish militias and their western backers to combat the jihadis in Syria and Iraq. Erdoğan has repeatedly dismissed the Syrian Kurdish Democratic Union party (PYD) and the Iraqi peshmerga as being no better than terrorists themselves, in league with Turkey’s Kurdistan Workers’ party (PKK).

Erdoğan renewed the Turkish state’s long-running conflict with the PKK last summer after his ruling Justice and Development party unexpectedly lost its parliamentary majority, largely due to the electoral success of the pro-Kurdish People’s Democratic party (HDP). He has since sought effectively to ban most HDP MPs from parliament while seeking to extend his presidential powers.

Large-scale crackdowns and curfews in Kurdish towns in the south-east have led to numerous deaths on both sides and mass civilian displacement. The violence provoked a spate of terrorist attacks on soft targets in Istanbul and Ankara by a militant PKK offshoot known as the Kurdistan Freedom Falcons (TAK).

The government says the TAK outrages prove the truth of its contention that the PKK is a purely terrorist organisation lacking legitimate cause that must be mercilessly extirpated. In recent months, conforming to this preferred narrative, attacks launched by Isis have been officially blamed, initially at least, on the Kurds, thereby confusing the overall picture and complicating the counter-terrorism response to Isis.

Incontrovertible evidence has now emerged that Isis operatives planned the Ankara attack last October. A total of 36 suspects are facing a total of up to 11,750 years in jail, according to the Ankara public prosecutor. It seems probable that Tuesday evening’s attack in Istanbul was Isis’s response to a recent wave of arrests and artillery bombardments targeting the group inside Turkey and across the border in Syria. Although it may not have thought so at the outset, Isis seems ever more persuaded in its view of Turkey as a hostile member of the US-led “crusader alliance”, and is punishing it accordingly.

Ministers have hitherto resisted suggestions that Isis runs cells and networks inside Turkey, but given the arrests this position is hardly tenable. The government is also unwilling to accept that its security and counter-terror intelligence-gathering arrangements are faulty, or that by degrees the country is being sucked ever further into Syria’s civil war – although both conclusions appear increasingly inescapable.

It seems plain that Erdoğan’s preference for blaming everything bad that happens on the Kurds is no longer working, that Turkish civilians are paying a terrible price for his wilful blindness to the jihadi threat, and that Turkey’s leaders must banish any remaining ambivalence and confront the Isis menace full on.

This week Ankara patched up relations with Russia and Israel, both strong anti-Isis actors, and stepped up border cooperation with Nato air patrols – an indication that attitudes may be changing. The logical corollary of such a shift is for Erdoğan to halt his war of choice against the PKK, reinstitute last year’s ceasefire, and accept that the price for a united front to defeat Isis terror and halt the Syrian carnage is a comprehensive settlement with the Kurds.